An air cleaner is sometimes used to clean, deodorize, or otherwise treat the air indoors and in vehicles, and particularly in closets, shoe cabinets, refrigerators, and kitchen cabinets. Air cleaners have been disclosed, for example, in JP-A 11-151443, JP-A 2001-253235, and JP-A 2002-253662.
There are known air cleaners that utilize a photocatalytic substance. Such air cleaners are have been disclosed, for example, in JP-A 11-151443 and JP-A 2002-253662.
FIG. 7 schematically illustrates a conventional air cleaner X2 that utilizes a photocatalytic substance. The air cleaner X2 comprises a housing 71, a dust filter 72, photocatalyst filters 73 and 74, an ultraviolet lamp 75, a fan 76, and a filter 77.
The housing 71 has an intake opening 71a and an exhaust opening 71b. The filter 72 is provided so as to block off the intake opening 71a, and the filter 77 is provided so as to block off the exhaust opening 71b. The photocatalytic filters 73 and 74 are composed of a nonwoven cloth to which powdered titanium oxide (TiO2) has been bonded, and functions when irradiated with the UV lamp 75. The fan 76 is provided on the exhaust opening 71b side, and actuating the fan 76 causes air to pass through the air cleaner X2. More specifically, when the fan 76 is actuated, air flows through the intake opening 71a and into the air cleaner X2, passes through the filter 72, the photocatalytic filters 73 and 74, and the filter 77 in that order, and then is exhausted from the air cleaner X2 via the exhaust opening 71b. Some semiconductor substances, such as titanium oxide, are known to have a photocatalytic function. Semiconductor substances having a photocatalytic function generally absorb light having energy corresponding to the bandgap of the valence band and the conduction band, which causes the electrons of the valence band to migrate to the conduction band, and this electron transition produces holes in the valence band. The electrons of the conduction band have the property of moving to a substance adsorbed to the surface of the photocatalytic functional semiconductor, and as a result this adsorbed substance can be reduced. The holes in the valence band have the property of stealing electrons from the substance adsorbed to the surface of the photocatalytic functional semiconductor, and as a result this adsorbed substance can be oxidized.
With titanium oxide (TiO2) having a photocatalytic function, the electrons that have migrated to the conduction band reduce the oxygen in the air and produce super-oxide anions (•O2−). Along with this, the holes produced in the valence band oxidize the adsorbed water on the titanium oxide surface and produce hydroxy radicals (•OH). Hydroxy radicals have an extremely powerful oxidation strength. Consequently, when an organic substance, for example, is adsorbed to photocatalytic titanium oxide, the action of the hydroxy radicals sometimes results in the organic substance being decomposed into water and carbon dioxide.
When the air cleaner X2 is operated, pollutants, microbes, and the like in the air are trapped in the photocatalytic filters 73 and 74. Since titanium oxide is adhered as a photocatalyst to the photocatalytic filters 73 and 74, as mentioned above, these pollutants, microbes, and so forth are subjected to a decomposing action in the photocatalytic filters 73 and 74 being irradiated with the UV lamp 75.
With this conventional air cleaner X2, the air has to be brought into contact very efficiently with the photocatalytic filters 73 and 74 in order to improve the air cleaning efficiency. This contact efficiency can be enhanced by increasing the surface area and/or thickness of the photocatalytic filters 73 and 74.
However, if the surface area of the photocatalytic filters 73 and 74 is increased, this tends to make the air cleaner X2 too bulky. Increasing the thickness of the photocatalytic filters 73 and 74 is also undesirable in terms of pressure loss when air passes through the photocatalytic filters 73 and 74. This is because when the thickness of the photocatalytic filters 73 and 74 is increased, there is a corresponding rise in the blower capacity required of the fan 76, and when the blower capacity of the fan 76 is raised, it is more difficult to keep the air cleaner X2 quiet.
Also, with the air cleaner X2, the amount of UV irradiation in the photocatalytic filters 73 and 74 is uneven. Specifically, the distance from the UV lamp 75 and the UV irradiation angle vary with the position on the photocatalytic filters 73 and 74. Accordingly, the decomposing action is insufficient in portions of the photocatalytic filters 73 and 74 where the amount of UV irradiation is small, and as a result, the intrinsic photocatalytic function had by the photocatalytic filters 73 and 74 cannot be fully realized with the conventional air cleaner X2.
The amount of UV irradiation can be made relatively uniform by increasing the number of UV lamps 75 installed, so it is possible to improve the photocatalytic function of the photocatalytic filters 73 and 74, and in turn to increase the air cleaning efficiency of the air cleaner X2. Nevertheless, with a configuration such as this, as the number of UV lamps 75 increases, so too does the number of inverters (not shown) needed to control the drive of these lamps and so forth, which ends up making the air cleaner X2 bulkier.
Thus, it was difficult to achieve high air cleaning efficiency while maintaining a small device size with the conventional air cleaner X2.